The present invention relates to a television signal scrambling method and apparatus which employ a scrambler for scrambling a television signal and a descrambler for restoring the scrambled television signal to its original unscrambled form.
Scrambling systems are well known in the art and are often employed in cable and other subscription TV systems for assuring that only paid subscribers receive the television signal transmissions to which they subscribe. A paid subscriber is provided with an authorized descrambler for unscrambling a scrambled television signal so that his television receiver may properly process the unscrambled television signal and allow him unimpeded reception. Non-subscribers, who do not have the appropriate descrambling equipment, will only receive the scrambled television signal which cannot be properly processed to produce an acceptable video and/or audio output.
All scrambling systems seek to provide an unintelligible video and/or audio signal to an unauthorized recipient which cannot be easily defeated or unscrambled without the proper descrambling equipment. The greater the sophisication of the scrambling provided, the more difficult it is for unauthorized recipients to replicate authorized descrambling equipment. However, as the sophistication of the scrambling technique increases, so does the cost of the associated scrambler and descrambler circuitry. Moreover, the more complex the circuit, the less reliable it becomes.
Some scrambling systems employ an addressing system whereby only particular descramblers are addressed and rendered operative to unscramble an incoming scrambled television signal. Addressing systems are typically complex making the overall scrambling system costly and unreliable.
The present invention has been designed to overcome the above problems associated with addressing scrambling systems, by providing a relatively inexpensive yet reliable addressing scrambling system.
One object of the invention is the provision of a scrambling system which can be used to identify and render operative predetermined descramblers, to the exclusion of others, using tier level coding information impressed on the scrambled television signal by the scrambler. Each descrambler detects the tier level coding information and, if it has be assigned a tier level code corresponding thereto, operates to descramble the incoming television signal.
An additional object of the invention is the provision of a scrambling system as described in the preceding paragraph wherein each of the descramblers contains a plug-in module which is programmable with the tier level code assigned thereto so that the assigned tier level code can be easily changed by changing the plug-in module.
An additional object of the invention is the provision of a scrambler which not only scrambles a television signal but which also impresses on the scrambled television signal tier level coding information within the bandwidth of the scrambled television signal which identifies and renders operative certain descramblers receiving the scrambled television signal.
An additional object of the invention is the provision of a scrambler as set forth in the preceding paragraph which can be easily programmed with particular tier level coding information.
An additional object of the invention is the provision of a descrambler which can be easily programmed with tier level coding information identifying it and which is able to receive a scrambled television signal containing tier level coding information therein and unscramble the scrambled television signal only if the tier level coding information contained therein coincides with the programmed tier level coding information.
An additional object of the invention is the provision of an addressable descrambler as described above which is capable of descrambling a scrambled television signal containing suppressed amplitude horizontal synchronizing signals and reconstructing timing pulses which are used to reconstruct the suppressed amplitude horizontal synchronizing signals.
These and other objects, features and advantages of the invention will become more readily apparent from the following description of the invention which is provided in conjunction with the attached drawings.